CA1166598A - Inhibitor for the polymerization of a 2- isocyanatoalkyl ester of an alpha, beta- ethylenically unsaturated carboxylic acid - Google Patents
Inhibitor for the polymerization of a 2- isocyanatoalkyl ester of an alpha, beta- ethylenically unsaturated carboxylic acidInfo
- Publication number
- CA1166598A CA1166598A CA000406602A CA406602A CA1166598A CA 1166598 A CA1166598 A CA 1166598A CA 000406602 A CA000406602 A CA 000406602A CA 406602 A CA406602 A CA 406602A CA 1166598 A CA1166598 A CA 1166598A
- Authority
- CA
- Canada
- Prior art keywords
- polymerization
- ester
- isocyanatoalkyl
- isocyanatoalkyl ester
- nitrogen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
This invention is directed to a process for distilling a 2-isocyanatoalkyl ester of an .alpha.,.beta.-ethyleni-cally unsaturated carboxylic acid from a liquid mixture.
The invention is characterized by distilling the isocyanatoalkyl ester in the presence of an amount of gaseous nitrogen oxide effective to inhibit the vinyl polymerization of the isocyanatoalkyl ester. The formation of a popcorn polymer is inhibited by the use of a nitrogen oxide.
28,838-F -11-
This invention is directed to a process for distilling a 2-isocyanatoalkyl ester of an .alpha.,.beta.-ethyleni-cally unsaturated carboxylic acid from a liquid mixture.
The invention is characterized by distilling the isocyanatoalkyl ester in the presence of an amount of gaseous nitrogen oxide effective to inhibit the vinyl polymerization of the isocyanatoalkyl ester. The formation of a popcorn polymer is inhibited by the use of a nitrogen oxide.
28,838-F -11-
Description
A PROCESS FOR DISTILLING
OF AN ~,~-ETHYLENICALLY
UNSATURATED CARBOXYLIC ACID
This invention relates to the use of ga~eous nitrogen dioxide or nitric oxide to inhibit the vinyl : polymerization of a 2-isocyanatoalkyl ester of an : N, ~-ethylenically unsaturated carboxylic acid.
: :
Certain conventional polymerization inhibitors have been used to inhibit during distillation the vinyl polymerization of a 2-isocyanatoalkyl ester of an ethylenically unsaturated carboxylic acid. For example, Europeani Patent Office Application Nv. 78190156.5, : I0 Publication No. 144,:published January 10, 1979, discloses : the use of phenothiazine to inhibit the polymerization of 2-lsocyanatoethyl methacrylate during distillation.
While conventional polymerization inhibitors :are generally effective in inhibiting polymerization of
OF AN ~,~-ETHYLENICALLY
UNSATURATED CARBOXYLIC ACID
This invention relates to the use of ga~eous nitrogen dioxide or nitric oxide to inhibit the vinyl : polymerization of a 2-isocyanatoalkyl ester of an : N, ~-ethylenically unsaturated carboxylic acid.
: :
Certain conventional polymerization inhibitors have been used to inhibit during distillation the vinyl polymerization of a 2-isocyanatoalkyl ester of an ethylenically unsaturated carboxylic acid. For example, Europeani Patent Office Application Nv. 78190156.5, : I0 Publication No. 144,:published January 10, 1979, discloses : the use of phenothiazine to inhibit the polymerization of 2-lsocyanatoethyl methacrylate during distillation.
While conventional polymerization inhibitors :are generally effective in inhibiting polymerization of
2:-isocyanatoalkyl esters during storage, they have not proven as effective during the distillation of the iso-; : cyanatoal]~yl ester. In particular, these isocyanatoalkylesters are susceptible to the formation of a hard, j ,: , ~ 28l838-F -1-.: ~ :
. i ~.~ ' ' .
- : .
--2~
brittle, highly cross~linked polymer, which is referred to as popcorn polymer in the prior art because of its physical appearance. This popcorn polymer is especially deleterious, because once formed it tends to initiate further polymerization.
Relatively volatile inhibitors, such as p-meth-oxyphenol, have been employed during the distillation of 2-isocyanatoalkyl methacrylate to inhibit polymer forma-tion in the gas phase and in the distillate. However, these volatile inhibitors have been observed to be rela-tively ineffective as polymerization inhibitors in this application.
Nitrogen oxides are known in the art to inhibit the polymerization of certain unsaturated compounds U.S. Patent 3,964,978 discloses the distillation of vinyl aromatic compounds in the presence of nitrogen dioxide to inhibit polymerization. U.S. Patent 3,964,979 teaches ; the use of nitric oxide to inhibit the polymerization of vinyl aromatic compounds during distillation. British Patent 1,265,419 teaches that acrylic acid can be distilled in the presence of nitric oxide in the gas phase and phenothiazine in the li~uid phase to minimize polymeriza-tion. Eowever, the presence o~ nitrogen dioxide is taught to promote the polymerization of acrylic acid and to discolor the distillate.
Nitric oxide is disclosed by J. F. Villa and H. B. Powellj Syn. React. Inorg. Metal-Org. Chem., 6, pp.
59-63 (1976), to catalyze the trimerization of certain aliphatic isocyanates. This disclosure suggests that nitric oxide would not be suitable as a polymerization inhibitor for a 2-isocyanatoalkyl ester.
28,838-F ~2 ' ' .. ~
'~
This invention is a process for distilling a 2-isocyanatoalkyl ester of an ~ ethylenically unsatu-rated carboxylic acid from a liquid mixture, character~
ized by distilling the isocyanatoalkyl ester in the presence of an amount of gaseous nitrogen oxide effective to inhibit the vinyl polymeriz.ation of the isocyanato-alkyl ester. An effective amount of the nitrogen oxide is an amount which reduces the polymerization of the isocyanatoalkyl ester compared to the polymerization which occurs at the same conditions in the absence of the nitrogen o~ide.
The 2-isocyanatoalkyl esters of ~ ethyleni-cally unsaturated carboxylic acids form a known class of compounds, which can be represented by the formula I
O ~R~
, ~
R'-C-O- C-~N=C=O
R
n wherein each R is indep~ndently hydrogen, alkyl, alkenyl, alkoxy, alkaryl, aral~yl or aryli R' is alkenyl; and n is 2 or 3. of course, R can represent a wide ~ariety of moieties, such as, methyl, ethyl, cyclohexyl, isopro-penyl, vinyl, etho~y, tolyl, phenylethyl or phenyl.
Preferably, R is hydrogen and n is 2. Preferably, R' is vinyl or isopropenyl, more preferably isopropenyl.
;~ Hereafter, the compound of formula I will be referred to as an isocyanatoalkyl ester for the sake of brevity.
The isocyanatoalkyl ester can be present in ~; 30 any mixture from which it can be separated by distilla-tion, so long as said mixture is substantially inert in 28,838-F -3--4~
the subject reaction. In order to conserve the nitrogen oxides added, diluents which may react with the nitrogen oxides are advantageously avoided. In one preferred embodiment, the isocyanatoalkyl ester to be distilled is prepared by reacting a 2-alkenyl-2-oxazoline or 2-alkenyl-2-oxazine in a water-immiscible solvent with phosgene in the presence of an aqueous hydrogen chloride acceptor, as is described in British Patent 1,252,099.
On completion of the phosgenation reaction, the organic phase containing the 2-isocyanatoalkyl ester is conven-iently separated and optionally dried with a conventional drying agent, such as CaCl2 or zeolite. The 2-isocyanato-alkyl ester of the unsaturated acid is then separated by distillation in the presence of a nitrogen oxide, as is disclosed hereinafter.
Nitrogen dioxide and nitric oxide, which are used as vinyl polymerization inhibitors herein, are both well-known compounds. For the sake of brevity these two polymerization inhibitors are hereafter referred to as nitrogen oxides. Either one of these nitrogen oxides, a mixture of such oxides or a diluent gas containing at least one of these oxides of nitrogen can be employed to inhibit polymerization. Mitric oxide is preferred as a polymerization inhi~itor ~ecause it adds fewer colored impurities to the typically colorless distilled isocyanatoalkyl ester than the other nitrogen oxides. Surprisingly, no isocyanate trimer is observed in the isocyanatoalkyl ester follow-ing treatment with nitric oxide. Any gaseous diluent used with the nitrogen oxides should be inert in the instant reaction. Preferably, the diluent gas is sub-stantially free of oxygen and water, more preferably the diluent gas, if present, is nitrogen.
: ~
28,838-F 4-: ~
-5~
The nitrogen oxide can operably be introduced in the region immediately above the liquid mass to be distilled to inhibit polymerization in the gas phase and in the liquid which condenses overhead. However, care must be taken in this embodiment to insure that the nitrogen oxide permeates the space above the medium or polymerization can occur. Of course, where a nitro-gen oxide is not introduced to the liquid medium, a polymerization inhibitor should al50 be employed in the liquid. However, some of the oxides of nitrogen inter~
act with other polymerization inhibitors to produce colored impurities. For example, p-methoxyphenol reacts with nitric oxide to produce a yellow-colored impurity, which will codistill with the isocyanatoalkyl lS ester, Less volatile polymerization inhibitors, such ~ as phenothiazine, may also form colored impurities, but - ~ these colored impurities typically will not distill with the isocyanatoalkyl ester. It is preferred, therefore, to sparge the nitrogèn oxide through the li~uid mixture during distillation and to use a polym-erization inhibitor in the mixture which is signifi-cantly less volatile than the isocyanatoalkyl ester.
~: :
If the distillation is conducted in a continu-,~
~ ous process, the nitrogen oxide can conveniently be ~: :
added to the incoming mixture containing the isocyanato-alkyl ester. The gaseous nitrogen oxides are virtually insoluble in the isocyanatoalkyl ester and these gases can be readily recovered and recycled. Generally, the inhibitor is gradually depleted during operation, but wlth recycle the intermittent replacement of only small amounts of the oxides o~ nitrogen is generally necessary.
' : :
: ~:
.
28,838-F -5-~ ~ , :
,~
The concentration of nitrogen oxides necessary to inhiblt polymerization varies over a wide range dependent upon numerous factors, including the identity of the nitrogen oxide and the isocyanatoalkyl ester, the distlllation temperature, the distillation pressure, residence time and the amount of reflux. Even the purity of the isocyanatoalkyl ester af~ects the forma-tion of polymers, as a crude starting material appears in general less susceptible to the formation of popcorn polymer during distillation than a comparatively pure isocyanatoalkyl ester. Generally, a concentration of nitric oxide in the gas phase immediately above the liquid medium of at least 0.01, preferably at least 0.02, more preferably at least 0.1 percent by weight, is efective to inhibit polymerization. At or near th~
minimum effective concentration care must be taken to see that the concentration is maintained uniformly above the liquid medium or else polymerization can occur. One convenient method distributing -the nitrogen oxide uniformly in a large volume is to introduce the nitrogen o~ide to the liquid in a diluent gas. The upper limit on the concentration of nitrogen oxide is ; ~ determined primarily by economic considerations. The ~; concentration of nitrogen oxides is preferably less than 20 percent, more preferably less than 3 percent by weight of the gases above the liquid distilled. At concentrations of nitrogen oxide greater than 2 percent by weight the distillate may be visibly colored.
:`:
The manner in which the distillation is car-ried out is not critical. The distillation is advanta-; geously conducted at reduced pressure, so as to avoid distillation at temperatures which are deleterious to ~` the isocyanatoalkyl ester. The distillation vessel ~` .
28,838-F -6-~"
~''` ~ ' :~ .
, ' should be closed, because some isocyanatoalkyl esters are very toxic, as are the oxides of nitrogen. Impuri-ties which are lower boiling than the isocyanatoalkyl ester are conveniently distilled before the 1socyanato-alkyl ester. Azeotropic mixtures can be created tomodify the order of distillation, if desired.
The temperature of the liquid during distil-lation is preferably from 65C to 110C, more preferably from 80~C to 95C. Higher temperatures than those in the preferred range, though op~rable, can result in poor separation and substantial decomposition or polym-erization of the isocyanatoalkyl ester at long residence times. Lower temperatures are not generally operable to distill the isocyanatoalkyl ester, even when dist11-lation is attempted under vacuum. Preferably, thepressure over the liquid to be distilled is from 5 to 15 millimeters of mercury (0.6-2.0 kPa~ during distillation.
The foIlowing examples are presented to illustrate the process of this invention, but are~ot to be taken as limiting its scope. All parts and percentages are by weight unless otherwise indicated.
.~
Example 1 To a round-bottom flask equipped with a ; 25 6 inch, straight tube distillation column topped with a distillation head, a means for stirring and a means for measuring temperature, was charged 121 grams of crude 2-i~ocyanatoethyl methacrylate (IEM) containing 82.2 percent IEM, 0.6 percent methylene chloride, 1080 parts ~ 30 per million (ppm) phenothiazine, less than 1 percent of ::
28,838-F -7-an epoxy resin, and a remaining amount of relatively non-volatile impurities resul-ting from the preparation of IEM. The epoxy resin reacts during distillation with the hydrolyzable chloride present to eliminate this impurity from the distilla-te.
The flask was heated to 95C under a pressure of lO mm of mercury (1.3 kPa), while the liquid was sparged with 20 cubic centimeters per minute of a nitrogen gas containing 0.8 percent nitric oxide. The IEM was refluxed for 1.25 hours and then distilled for 2 hours. Assuming a constant rate of distillation, the concentration of nitric oxide in the gas phase was 376 ppm.
, The distillate recovered was analyzed by con-ventional gas and liquid chromatographic techniques and was found to be essentially pure monomeric IEM. The 85 grams of distillate recovered represented a yield of 70 pe~cent. The undistilled tars were clear fluids. No popcorn polymer was observed.
Comparative_Experiment In -the manner described in Example 1, 50 ` grams of crude IEM was refluxed at 95C under a pressure of 10 mm ~f mercury (1.3 kPa), except that no nitric ~ oxide was introduced. After 15 minutes of heating, ; 25 popcorn polymer was observed in the column and the flask. After an additional hour, the entire contents ~; of the flask polymerized.
Exam~le 2 In a manner otherwise identical to Example 1, pure nitric oxide was sparged through the crude IEM, 28,838-F -8-' while the IEM was first refluxed at 95C for 1 hour and then distilled over a period of 2 hours. No popcorn polymer was observed in either the distillate or the undistilled material.
Example 3 In a manner otherwise similar to Example 2, 204.4 grams of crude IEM, containing 86.6 percent IEM
and 700 ppm pheno-thiazine, were refluxed at 90~C for 1 hour and then distilled. During reflux and distilla-tion, a nitrogen gas stream containing 0.8 percentnitric oxide was introduced to the distillation vessel immediately above the liquid medium. Two and one-half hours after the reflux was initiated, all of the material remaining in the flask was popcorn polymer. The distil-late contained 112.5 grams of essentially pure IEM,representing a yield of 55 percent.
:
Example 4 In a manner similar to Example 1, 151 grams of crude IEM, containing 81 percent IEM, 1000 ppm phenothiazine and small amounts of methyIene chloride ~` and an epoxy resin, were refluxed at 92C under a pressure of 9 millimeters of mercury, while a gaseous mixture con-taining 0.16 percent nitxogen dioxide in nitrogen was sparged through the liquid. The gas was passed through the liquid at a rate of 168.8 cubic centimeters per minu-te. A~ter 2 hours, distillation of the gas-sparged liquid was initiated. Over a period of
. i ~.~ ' ' .
- : .
--2~
brittle, highly cross~linked polymer, which is referred to as popcorn polymer in the prior art because of its physical appearance. This popcorn polymer is especially deleterious, because once formed it tends to initiate further polymerization.
Relatively volatile inhibitors, such as p-meth-oxyphenol, have been employed during the distillation of 2-isocyanatoalkyl methacrylate to inhibit polymer forma-tion in the gas phase and in the distillate. However, these volatile inhibitors have been observed to be rela-tively ineffective as polymerization inhibitors in this application.
Nitrogen oxides are known in the art to inhibit the polymerization of certain unsaturated compounds U.S. Patent 3,964,978 discloses the distillation of vinyl aromatic compounds in the presence of nitrogen dioxide to inhibit polymerization. U.S. Patent 3,964,979 teaches ; the use of nitric oxide to inhibit the polymerization of vinyl aromatic compounds during distillation. British Patent 1,265,419 teaches that acrylic acid can be distilled in the presence of nitric oxide in the gas phase and phenothiazine in the li~uid phase to minimize polymeriza-tion. Eowever, the presence o~ nitrogen dioxide is taught to promote the polymerization of acrylic acid and to discolor the distillate.
Nitric oxide is disclosed by J. F. Villa and H. B. Powellj Syn. React. Inorg. Metal-Org. Chem., 6, pp.
59-63 (1976), to catalyze the trimerization of certain aliphatic isocyanates. This disclosure suggests that nitric oxide would not be suitable as a polymerization inhibitor for a 2-isocyanatoalkyl ester.
28,838-F ~2 ' ' .. ~
'~
This invention is a process for distilling a 2-isocyanatoalkyl ester of an ~ ethylenically unsatu-rated carboxylic acid from a liquid mixture, character~
ized by distilling the isocyanatoalkyl ester in the presence of an amount of gaseous nitrogen oxide effective to inhibit the vinyl polymeriz.ation of the isocyanato-alkyl ester. An effective amount of the nitrogen oxide is an amount which reduces the polymerization of the isocyanatoalkyl ester compared to the polymerization which occurs at the same conditions in the absence of the nitrogen o~ide.
The 2-isocyanatoalkyl esters of ~ ethyleni-cally unsaturated carboxylic acids form a known class of compounds, which can be represented by the formula I
O ~R~
, ~
R'-C-O- C-~N=C=O
R
n wherein each R is indep~ndently hydrogen, alkyl, alkenyl, alkoxy, alkaryl, aral~yl or aryli R' is alkenyl; and n is 2 or 3. of course, R can represent a wide ~ariety of moieties, such as, methyl, ethyl, cyclohexyl, isopro-penyl, vinyl, etho~y, tolyl, phenylethyl or phenyl.
Preferably, R is hydrogen and n is 2. Preferably, R' is vinyl or isopropenyl, more preferably isopropenyl.
;~ Hereafter, the compound of formula I will be referred to as an isocyanatoalkyl ester for the sake of brevity.
The isocyanatoalkyl ester can be present in ~; 30 any mixture from which it can be separated by distilla-tion, so long as said mixture is substantially inert in 28,838-F -3--4~
the subject reaction. In order to conserve the nitrogen oxides added, diluents which may react with the nitrogen oxides are advantageously avoided. In one preferred embodiment, the isocyanatoalkyl ester to be distilled is prepared by reacting a 2-alkenyl-2-oxazoline or 2-alkenyl-2-oxazine in a water-immiscible solvent with phosgene in the presence of an aqueous hydrogen chloride acceptor, as is described in British Patent 1,252,099.
On completion of the phosgenation reaction, the organic phase containing the 2-isocyanatoalkyl ester is conven-iently separated and optionally dried with a conventional drying agent, such as CaCl2 or zeolite. The 2-isocyanato-alkyl ester of the unsaturated acid is then separated by distillation in the presence of a nitrogen oxide, as is disclosed hereinafter.
Nitrogen dioxide and nitric oxide, which are used as vinyl polymerization inhibitors herein, are both well-known compounds. For the sake of brevity these two polymerization inhibitors are hereafter referred to as nitrogen oxides. Either one of these nitrogen oxides, a mixture of such oxides or a diluent gas containing at least one of these oxides of nitrogen can be employed to inhibit polymerization. Mitric oxide is preferred as a polymerization inhi~itor ~ecause it adds fewer colored impurities to the typically colorless distilled isocyanatoalkyl ester than the other nitrogen oxides. Surprisingly, no isocyanate trimer is observed in the isocyanatoalkyl ester follow-ing treatment with nitric oxide. Any gaseous diluent used with the nitrogen oxides should be inert in the instant reaction. Preferably, the diluent gas is sub-stantially free of oxygen and water, more preferably the diluent gas, if present, is nitrogen.
: ~
28,838-F 4-: ~
-5~
The nitrogen oxide can operably be introduced in the region immediately above the liquid mass to be distilled to inhibit polymerization in the gas phase and in the liquid which condenses overhead. However, care must be taken in this embodiment to insure that the nitrogen oxide permeates the space above the medium or polymerization can occur. Of course, where a nitro-gen oxide is not introduced to the liquid medium, a polymerization inhibitor should al50 be employed in the liquid. However, some of the oxides of nitrogen inter~
act with other polymerization inhibitors to produce colored impurities. For example, p-methoxyphenol reacts with nitric oxide to produce a yellow-colored impurity, which will codistill with the isocyanatoalkyl lS ester, Less volatile polymerization inhibitors, such ~ as phenothiazine, may also form colored impurities, but - ~ these colored impurities typically will not distill with the isocyanatoalkyl ester. It is preferred, therefore, to sparge the nitrogèn oxide through the li~uid mixture during distillation and to use a polym-erization inhibitor in the mixture which is signifi-cantly less volatile than the isocyanatoalkyl ester.
~: :
If the distillation is conducted in a continu-,~
~ ous process, the nitrogen oxide can conveniently be ~: :
added to the incoming mixture containing the isocyanato-alkyl ester. The gaseous nitrogen oxides are virtually insoluble in the isocyanatoalkyl ester and these gases can be readily recovered and recycled. Generally, the inhibitor is gradually depleted during operation, but wlth recycle the intermittent replacement of only small amounts of the oxides o~ nitrogen is generally necessary.
' : :
: ~:
.
28,838-F -5-~ ~ , :
,~
The concentration of nitrogen oxides necessary to inhiblt polymerization varies over a wide range dependent upon numerous factors, including the identity of the nitrogen oxide and the isocyanatoalkyl ester, the distlllation temperature, the distillation pressure, residence time and the amount of reflux. Even the purity of the isocyanatoalkyl ester af~ects the forma-tion of polymers, as a crude starting material appears in general less susceptible to the formation of popcorn polymer during distillation than a comparatively pure isocyanatoalkyl ester. Generally, a concentration of nitric oxide in the gas phase immediately above the liquid medium of at least 0.01, preferably at least 0.02, more preferably at least 0.1 percent by weight, is efective to inhibit polymerization. At or near th~
minimum effective concentration care must be taken to see that the concentration is maintained uniformly above the liquid medium or else polymerization can occur. One convenient method distributing -the nitrogen oxide uniformly in a large volume is to introduce the nitrogen o~ide to the liquid in a diluent gas. The upper limit on the concentration of nitrogen oxide is ; ~ determined primarily by economic considerations. The ~; concentration of nitrogen oxides is preferably less than 20 percent, more preferably less than 3 percent by weight of the gases above the liquid distilled. At concentrations of nitrogen oxide greater than 2 percent by weight the distillate may be visibly colored.
:`:
The manner in which the distillation is car-ried out is not critical. The distillation is advanta-; geously conducted at reduced pressure, so as to avoid distillation at temperatures which are deleterious to ~` the isocyanatoalkyl ester. The distillation vessel ~` .
28,838-F -6-~"
~''` ~ ' :~ .
, ' should be closed, because some isocyanatoalkyl esters are very toxic, as are the oxides of nitrogen. Impuri-ties which are lower boiling than the isocyanatoalkyl ester are conveniently distilled before the 1socyanato-alkyl ester. Azeotropic mixtures can be created tomodify the order of distillation, if desired.
The temperature of the liquid during distil-lation is preferably from 65C to 110C, more preferably from 80~C to 95C. Higher temperatures than those in the preferred range, though op~rable, can result in poor separation and substantial decomposition or polym-erization of the isocyanatoalkyl ester at long residence times. Lower temperatures are not generally operable to distill the isocyanatoalkyl ester, even when dist11-lation is attempted under vacuum. Preferably, thepressure over the liquid to be distilled is from 5 to 15 millimeters of mercury (0.6-2.0 kPa~ during distillation.
The foIlowing examples are presented to illustrate the process of this invention, but are~ot to be taken as limiting its scope. All parts and percentages are by weight unless otherwise indicated.
.~
Example 1 To a round-bottom flask equipped with a ; 25 6 inch, straight tube distillation column topped with a distillation head, a means for stirring and a means for measuring temperature, was charged 121 grams of crude 2-i~ocyanatoethyl methacrylate (IEM) containing 82.2 percent IEM, 0.6 percent methylene chloride, 1080 parts ~ 30 per million (ppm) phenothiazine, less than 1 percent of ::
28,838-F -7-an epoxy resin, and a remaining amount of relatively non-volatile impurities resul-ting from the preparation of IEM. The epoxy resin reacts during distillation with the hydrolyzable chloride present to eliminate this impurity from the distilla-te.
The flask was heated to 95C under a pressure of lO mm of mercury (1.3 kPa), while the liquid was sparged with 20 cubic centimeters per minute of a nitrogen gas containing 0.8 percent nitric oxide. The IEM was refluxed for 1.25 hours and then distilled for 2 hours. Assuming a constant rate of distillation, the concentration of nitric oxide in the gas phase was 376 ppm.
, The distillate recovered was analyzed by con-ventional gas and liquid chromatographic techniques and was found to be essentially pure monomeric IEM. The 85 grams of distillate recovered represented a yield of 70 pe~cent. The undistilled tars were clear fluids. No popcorn polymer was observed.
Comparative_Experiment In -the manner described in Example 1, 50 ` grams of crude IEM was refluxed at 95C under a pressure of 10 mm ~f mercury (1.3 kPa), except that no nitric ~ oxide was introduced. After 15 minutes of heating, ; 25 popcorn polymer was observed in the column and the flask. After an additional hour, the entire contents ~; of the flask polymerized.
Exam~le 2 In a manner otherwise identical to Example 1, pure nitric oxide was sparged through the crude IEM, 28,838-F -8-' while the IEM was first refluxed at 95C for 1 hour and then distilled over a period of 2 hours. No popcorn polymer was observed in either the distillate or the undistilled material.
Example 3 In a manner otherwise similar to Example 2, 204.4 grams of crude IEM, containing 86.6 percent IEM
and 700 ppm pheno-thiazine, were refluxed at 90~C for 1 hour and then distilled. During reflux and distilla-tion, a nitrogen gas stream containing 0.8 percentnitric oxide was introduced to the distillation vessel immediately above the liquid medium. Two and one-half hours after the reflux was initiated, all of the material remaining in the flask was popcorn polymer. The distil-late contained 112.5 grams of essentially pure IEM,representing a yield of 55 percent.
:
Example 4 In a manner similar to Example 1, 151 grams of crude IEM, containing 81 percent IEM, 1000 ppm phenothiazine and small amounts of methyIene chloride ~` and an epoxy resin, were refluxed at 92C under a pressure of 9 millimeters of mercury, while a gaseous mixture con-taining 0.16 percent nitxogen dioxide in nitrogen was sparged through the liquid. The gas was passed through the liquid at a rate of 168.8 cubic centimeters per minu-te. A~ter 2 hours, distillation of the gas-sparged liquid was initiated. Over a period of
3 hours, 85.6 grams of essentially pure IEM was recovered in th distillate, representing a yield of 70 percent.
The undistilled residue remained fluid and no popcorn polymer was produced in the system.
~' ~
~ ; 28,838-F -9-~ ' ~ .
: `
The undistilled residue remained fluid and no popcorn polymer was produced in the system.
~' ~
~ ; 28,838-F -9-~ ' ~ .
: `
Claims (5)
1. A process for distilling a 2-isocya-natoalkyl ester of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid from a liquid mixture, characterized by distilling the isocyanatoalkyl ester in the presence of an amount of gaseous nitrogen oxide effective to inhibit the vinyl polymerization of the isocyanatoalkyl ester.
2. The process as described in Claim 1 characterized in that the nitrogen oxide is nitric oxide.
3. The process as described in Claim 2 characterized in that the distillation is conducted in an oxygen-free atmosphere.
4. The process as described in Claim 2 characterized in that the nitric oxide is sparged through the liquid mixture.
5. The process as described in Claim 4 characterized in that the concentration of nitric oxide in the gas phase immediately above the liquid is from 0.01 to 3 percent by weight.
28,838 F -10-
28,838 F -10-
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000406602A CA1166598A (en) | 1982-07-05 | 1982-07-05 | Inhibitor for the polymerization of a 2- isocyanatoalkyl ester of an alpha, beta- ethylenically unsaturated carboxylic acid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000406602A CA1166598A (en) | 1982-07-05 | 1982-07-05 | Inhibitor for the polymerization of a 2- isocyanatoalkyl ester of an alpha, beta- ethylenically unsaturated carboxylic acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1166598A true CA1166598A (en) | 1984-05-01 |
Family
ID=4123149
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406602A Expired CA1166598A (en) | 1982-07-05 | 1982-07-05 | Inhibitor for the polymerization of a 2- isocyanatoalkyl ester of an alpha, beta- ethylenically unsaturated carboxylic acid |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1166598A (en) |
-
1982
- 1982-07-05 CA CA000406602A patent/CA1166598A/en not_active Expired
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